This invention relates to a thermally actuated valve assembly and more particularly to a dual function thermal vacuum valve useful for instance in automotive emission control systems. Various thermally actuated valves have been used for automotive applications. For example, wax actuated valves have long been used. These valves consist of a spool valve which is actuated by a volume change of wax upon reaching a predetermined temperature. These valves, however, due to the high pressure build-up are subject to loss of wax and consequently a shift of operating temperature and are actuable at only one temperature. Additionally they are costly to manufacture.
Dual function valves incorporating a bimetallic disc as the actuating means such as described in co-pending application Ser. No. 530,800, entitled Double Throw Thermal Valve, filed Dec. 9, 1974, having the same assignee as the present application have also been used. Their use has proved successful but still these valves have the inherent disadvantage for certain applications of being actuable at only one temperature.
It is an object of this invention to provide a thermally responsive valve assembly actuable at more than one temperature. It is another object to provide a thermally responsive dual function valve which is compact in size, reliable and to which three pieces of tubing or the like may be readily connected at one end of the valve assembly. It is yet another object to provide a valve assembly which minimizes deleterious compression of elastomeric valve seal means. Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.
Briefly the double throw thermally responsive valve assembly of this invention comprises a two part valve body, a first part having three ports extending from the valve body and a second part with a central cavity in which the first part is partially housed. In the first part, passages connect the respective ports to a common chamber and valve seats are formed around two of the passages at the top and bottom of the chamber respectively. In the bottom of the cavity in the second part, a stop or support post is disposed upon which a multi-member thermostatic disc assembly is mounted. The assembly comprises two preformed thermostatic disc members with a spring member between contained within a disc carrier or housing member. The two disc members are provided to be actuable at different predetermined temperatures. Touching the top of the disc assembly is a motion transfer pin which is biased toward the disc by a spring. The transfer pin extends up out of the second part of the valve body into the chamber in the first part to contact a valve plug or rubber stopper which acts as a valve seal for both a top and a bottom valve seat.
Initially, in a first temperature range, engagement of the disc assembly with the support post and the transfer pin holds the rubber stopper plug or valve seal in position to engage and close off the top valve seat providing for communication only between ports two and three. At a predetermined second temperature, one of the disc members snaps to an inverted dish-shaped configuration which causes the valve seal to move out of engagement with the first top valve seat and to also hold the seal out of engagement with the bottom valve seat thereby providing communication among ports one, two, and three. Then at a third predetermined temperature, the second of the disc members snaps to an inverted dish-shaped configuration which causes the valve seal to come into engagement with the bottom valve seat thereby providing communication between only ports one and two.